1. Field of the Invention
The present invention relates to a magnetic sensor device such as a magnetic sensor that includes a magnetoresistance element for sensing a motion of a magnetic member.
2. Description of Related Art
An example of a magnetic sensor is disclosed in JP-A-9-196701. A relevant portion of the magnetic sensor is illustrated in FIGS. 9 and 10 attached hereto. The magnetic sensor includes a sensor chip 31 having a first MRE pair 1 consisting of magnetoresistance elements MRE1 and MRE2, and a second MRE pair 2 consisting of magnetoresistance elements MRE3 and MRE4. The sensor chip 31 is positioned to face a rotor RT having teeth made of a magnetic material. The sensor chip 31 and a circuit chip 32 that amplifies signals from the sensor chip 31 and/or converting the signals to binary signals are mounted on a reed frame 33 and molded together with molding resin 34, forming a molded unit. A power source terminal T1, an output terminal T2 and a ground terminal T3 are led out from the molded unit.
The magnetic sensor also includes a biasing magnet 35 that has a groove 35a extending in the longitudinal direction of the biasing magnet 35a. The molded unit including the sensor chip 31 and the circuit 32 is mounted on a bottom surface of the groove 35a and pasted with adhesive. Thus, magnetoresistance elements in the sensor chip 31 are placed in a biasing magnetic field.
According to rotation of the rotor RT, a magnetic field, in which the magnetoresistance elements MRE1-MRE4 are placed, changes. Electrical resistances of these elements vary in response to changes in the magnetic field. A rotational speed of the rotor RT is detected as changes in the electrical resistances of the magnetoresistance elements. MRE1-MRE4 form a bridge circuit, and outputs from the bridge circuit are processed by the circuit chip 32 and taken out from the output terminal T2.
Components of the magnetic sensor such as the sensor chip 31 and the circuit chip 32 are mounted on a reed frame 33 and molded together, forming a molded unit. Then, molded unit is mounted on the magnet 35. Alternatively, the components are connected to a printed circuit board, and then the circuit board is mounted on the magnet 35. In such a conventional structure, a reed frame or a circuit board for mounting components thereon is anyway required, resulting in increase in manufacturing costs.